1. Field of the Invention
This invention generally relates to a superconductor and a method of fabricating a superconductor. This invention specifically relates to a copper oxide superconductor. This invention also relates to a thin-film superconductor.
2. Description of the Prior Art
J. G. Bednorz and K. A. Muller discovered a high-Tc superconductor including a perovskite oxide compound of the Ba--La--Cu--O system (J. G. Bednorz and K. A. Muller: Zeitshrift Fur Physik B, Condensed Matter, Vol. 64, 189-193, 1986). After the discovery by J. G. Bednorz and K. A. Muller, other perovskite oxide superconductors have also been discovered which have various chemical compositions.
S. N. Putilin et al discovered that a mercury-bearing perovskite oxide compound of HgBa.sub.2 CuO.sub.4+.delta. was superconducting below a temperature of 94 K. (S. N. Putilin et al: Nature, Vol. 362, p. 226, 1993). This superconducting oxide compound is thought to be of a crystal structure in which perovskite Ba.sub.2 CuO.sub.4 layers containing CuO.sub.6 octahedrons are separated by 1-atom layers mainly containing mercury atoms. It should be noted that 1-atom layers mean layers having thicknesses corresponding to one atom.
When the HgBa.sub.2 CuO.sub.4+.delta. superconductor is practically used and operated as a superconductor at the liquid nitrogen temperature (77 K.), its superconducting transition temperature Tc being 94 K. is close to the lower limit of a usable transition temperature range in consideration of a necessary temperature margin. Accordingly, superconducting transition temperatures Tc higher than 94 K. are desirable for sure use and operation of superconductors at the liquid nitrogen temperature.
Since a mercury vapor pressure is very high, mercury-containing oxide compounds are generally made in a sealed container where oxygen gas and mercury vapor are held in pressurized states. Such methods of making mercury-containing oxide compounds are complicated, and thus have a problem in industrial application thereof.
Available HgBa.sub.2 CuO.sub.4+.delta. superconductors are only in the form of ceramics. One reason for this fact is that a mercury vapor pressure is very high. Generally, thin-film configurations of superconductors are desirable for their applications to electronic devices. Accordingly, thin-films of HgBa.sub.2 CuO.sub.4+.delta. superconductors have been desired.
Furthermore, regarding applications of thin-film oxide superconductors to electronic devices, each of the superconductors is sometimes required to be made of a single crystal without grain boundaries. Some cases require a laminate of a thin-film oxide superconductor and a layer of other material. To meet such requirements, it has been desired to realize "in-situ growth" where a thin film is formed on a heated substrate, and the thin film is provided with a crystal structure upon the formation thereof as in the fabrication of known YBa.sub.2 Cu.sub.3 O.sub.7 superconductors.